Eating about one serving per day of green, leafy vegetables may be linked to a slower rate of brain aging, according to a study.

It found that people who ate at least one serving of green, leafy vegetables a day had a slower rate of decline on tests of memory and thinking skills than people who never or rarely ate these vegetables.

The difference between the two groups was the equivalent of being 11 years younger in age, according to study author Martha Clare Morris, ScD, of Rush University Medical Center in Chicago.

“Adding a daily serving of green, leafy vegetables to your diet may be a simple way to foster your brain health,” said Morris.

“Projections show sharp increases in the percentage of people with dementia as the oldest age groups continue to grow in number, so effective strategies to prevent dementia are critical.”

The study involved 960 people with an average age of 81 who did not have dementia and were followed for an average of 4.7 years. The participants completed a questionnaire about how often they ate certain foods and had their thinking and memory skills tested yearly during that time.

The questionnaire asked how often and how many servings people ate of three green, leafy vegetables: spinach, with a serving being a half cup of cooked spinach; kale/collards/greens, half cup cooked; and lettuce salad, with a serving of one cup raw.

The participants were divided into five equal groups based on how often they ate green, leafy vegetables. The people in the top serving group ate an average of about 1.3 servings per day. Those in the lowest serving group ate on average 0.1 servings per day.

Overall, the participants’ scores on the thinking and memory tests declined over time at a rate of 0.08 standardized units per year. Over 10 years of follow-up, the rate of decline for those who ate the most leafy greens was slower by 0.05 standardized units per year than the rate for those who ate the least leafy greens. This difference was equivalent to being 11 years younger in age.

The results remained valid after accounting for other factors that could affect brain health such as smoking, high blood pressure, obesity, education level and amount of physical and cognitive activities.

Morris noted that the study does not prove that eating green, leafy vegetables slows brain aging, it only shows an association. She also said that the study cannot rule out other possible reasons for the link. In addition, Morris said that because the study focused on older adults and the majority of participants were white, the results may not apply to younger adults and people of colour.